Forget your plan, just call done_testing

I am not a fan of it, as I really like when my script knows how many tests it is going to run,
but sometimes it is really difficult to know up-front. It might depend on the number of
files in a directory. We might be able to compute the number at the beginning of our test-script,
but in some case this might be too difficult with a lot of value.

The output of such test-script is quite similar to the case when we used no_plan.

ok 1 - 1+1
ok 2 - 2+2
1..2

The difference is that in this case we explicitely need to tell the testing environment that we have finished all the
tests. This means if we exit() early, even the line immediately before done_testing()
we won't get the plan printed at the end, instead we'll have a comment:

perl test.t

ok 1 - 1+1
ok 2 - 2+2
# Tests were run but no plan was declared and done_testing() was not seen.